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keying and the sizzle…
hey all,
I have some footage that I have begun keying, and am noticing that on certain shadowed areas, I am getting the “sizzle”. I have tried a few different techniques, using just keylight vs. channel keying, and not much difference. I hope everyone is familiar with this, where the footage looks like it’s frying. Now, I thought using ‘Remove Grain’ would work, but it’s not really doing much. Any ideas on some processes I can try to get rid of it? I’m trying not to rotoscope it out, but if I have to, I will.Thanks,
Francisco -
8 Replies
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Usually the sizzle is caused by heavy-handed key settings. This is not to say you are doing anything wrong per se, some greenscreen plates require stronger settings to get everything keyed out. But this is usually a sign of quality problems with the footage – the video’s lighting wasn’t done properly, you are working with DV footage etc.
If it IS a quality issue, your options are more limited. Seeing a frame of your footage without any keying applied would really help in making a recommendation, because different techniques are required for different situations.
Brendan Coots
Splitvision Digital
http://www.splitvisiondigital.com -
also keep in mind that Keylight uses a default gray color for replacing spill during spill removal…sometimes changing this color to match your subject or background. Using the Status view, you can see areas in which keylight is manipulating as they will show up as a light green in a otherwise black and white image.
There are a couple of tutorials around such as the “super tight junk mattes” tutorial, which will help you eliminate much of your background so that you are only keying on a small amount around your subject. Allowing you to be a little more specific and lenient with your keying settings.Erik
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Dave’s approach seems to be like a good starting off point, I’ll try that next. Below is the screen grab. I have adjusted the grade in Color to get a more uniform green for the key. Once I get a good key, I plan on color correcting the footage again to match the composition. The “sizzle” is happening underneath the bike. Let me know what you think.
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Don’t color correct first!
Keylight is a color difference keyer, meaning that it requires a strong difference between the color of your greenscreen and the color of your foreground element to work. When you color correct, your changes apply to the entire image so you aren’t really enhancing the color differences, just shifting things around – an exercise in futility. The goal is not necessarily a strong green background, but a strong difference between its color and that of the foreground.
Ultimately the biggest obstacle with your footage is the green spill on the motorcycle and stand (since they are metallic), which is surely being affected by your color correction just as much as the background plate.
Brendan Coots
Splitvision Digital
http://www.splitvisiondigital.com -
Thanks for all the help. I think a animated mask along with some composition work later on will get rid of the sizzle. I color corrected first to even out the greenscreen. The lighting was a bit off, so the Color application really did a nice job of isolating the areas I wanted to adjust. After that, I got an awesome key with little effort, so I don’t think it was all for nothing. The metal is proving to be tricky, but with a spill supressor, it’s looking good.
Thanks for all the help, the Cow rocks!
-Francisco
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[beenyweenies] “The goal is not necessarily a strong green background, but a strong difference between its color and that of the foreground.”
I thought I should also mention that the goal is a strong difference in the HUE between the foreground and the background =)
Darby Edelen
DVD Menu Artist
Left Coast Digital
Aptos, CA -
Well, yeah. I said “color” because it’s really both hue AND saturation that the keyer draws upon. In my mind, hue+saturation=color.
Brendan Coots
Splitvision Digital
http://www.splitvisiondigital.com -
[beenyweenies] “Well, yeah. I said “color” because it’s really both hue AND saturation that the keyer draws upon. In my mind, hue+saturation=color.”
True, saturation comes into play in edges/semi-transparent sections and despilling, but in my mind the saturation is secondary to hue. If the pixel isn’t of a similar hue to the key color then it (obviously) won’t be touched at all and the saturation will never be examined.
Darby Edelen
DVD Menu Artist
Left Coast Digital
Aptos, CA
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